Vietnam is just a small part of the story. The games story is set across a large period of time.
Some of the singleplayer maps are based on multiplayer maps, which is usually the other way around.
In some missions...
For your enjoyment:
What platforms is Final Fantasy 14 coming to?
Currently the game is confirmed for PlayStation 3 and Windows PC. An Xbox 360 version isn't official, but Square Enix is considering the possibility that it could.